Tuesday, April 22, 2014

New paper finds solar UV is correlated to global mean temperature

A paper published today in Methods in Ecology and Evolution describes a new satellite dataset of solar UV-B radiation for use in ecological studies. According to the authors, "UV-B surfaces were correlated with global mean temperature and annual mean radiation data, but exhibited variable spatial associations across the globe." The finding is notable, since climate scientists dismiss the role of the Sun in climate change by only looking at the tiny 0.1% variations in total solar irradiance [TSI] over solar cycles, ignoring the large variations in solar UV of up to 100% over solar cycles, and which according to this paper, correlates to global mean temperature. Thus, the role of the Sun and solar amplification mechanisms on climate is only at the earliest stages of understanding.

Macroecology has prospered in recent years due in part to the wide array of climatic data, such as those provided by the WorldClim and CliMond data sets, which has become available for research. However, important environmental variables have still been missing, including spatial data sets on UV-B radiation, an increasingly recognized driver of ecological processes.

We developed a set of global UV-B surfaces (glUV) suitable to match common spatial scales in macroecology. Our data set is based on remotely sensed records from NASA's Ozone Monitoring Instrument (Aura-OMI). Following a similar approach as for the WorldClim and CliMond data sets, we processed daily UV-B measurements acquired over a period of eight years into monthly mean UV-B data and six ecologically meaningful UV-B variables with a 15-arc minute resolution. These bioclimatic variables represent Annual Mean UV-B, UV-B Seasonality, Mean UV-B of Highest Month, Mean UV-B of Lowest Month, Sum of Monthly Mean UV-B during Highest Quarter and Sum of Monthly Mean UV-B during Lowest Quarter. We correlated our data sets with selected variables of existing bioclimatic surfaces for land and with Terra–MODIS Sea Surface Temperature for ocean regions to test for relations to known gradients and patterns.

UV-B surfaces showed a distinct seasonal variance at a global scale, while the intensity of UV-B radiation decreased towards higher latitudes and was modified by topographic and climatic heterogeneity. UV-B surfaces were correlated with global mean temperature and annual mean radiation data, but exhibited variable spatial associations across the globe. UV-B surfaces were otherwise widely independent of existing bioclimatic surfaces.

Our data set provides new climatological information relevant for macroecological analyses. As UV-B is a known driver of numerous biological patterns and processes, our data set offers the potential to generate a better understanding of these dynamics in macroecology, biogeography, global change research and beyond. The glUV data set containing monthly mean UV-B data and six derived UV-B surfaces is freely available for download at: http://www.ufz.de/gluv.

UPDATE: see comment below 4/24/14

2 comments:

The words you have highlighted from the abstract (in your title),“UV-B surfaces were correlated with global mean temperature and annual mean radiation data” have two possible meanings. We’re used to thinking of time correlation of spatial means. But it can equally mean spatial correlation of time means. Since they have cited a dataset of spatially distributed time mean temperatures, and used LISA to get the spatial correlations, it’s clear that they are using the second interpretation."

Nick was able to determine this from a read of the full paper, therefore, I requested confirmation and a copy of the full paper from the authors, received this morning. The authors confirm the paper shows a correlation between spatial UV-B and spatial mean annual temperature and that they did not test for temporal correlations. Thus, the abstract was incorrectly/misleadingly worded as finding

"UV-B surfaces were correlated with global mean temperature"

when it would have been more correct to state

"UV-B surfaces were correlated with spatial mean temperature"

as use of the term "global" to describe a spatial mean temperature is inappropriate.

Thus, based upon the now-clarified although inappropriate wording of the abstract, the claim of this post that UV-B is correlated to "global mean temperature" is withdrawn.

Nonetheless, there could still be a correlation between the two and should be investigated for some of the following reasons:

1. Solar UV varies up to 100% over solar cycles2. Solar UV greatly affects a) ozone production, which can also act as one of many solar amplification mechanismsb) temperatures of the stratosphere, mesosphere, thermospherec) photosynthesis and other large effects on the biosphere as shown by this paperd) UV is the most energetic portion of the solar spectrum, and penetrates the deepest into the ocean compared to the rest of the solar spectrum. Therefore, it has the greatest effect upon ocean heating compared to any other portion of the solar spectrum, and likely is more efficient in heating land as well.

These are just a few of the reasons why the effects of the Sun on climate are at the very earliest stages of understanding and unfortunately continue to be ignored by climate modelers.

"The words you have highlighted from the abstract (in your title),“UV-B surfaces were correlated with global mean temperature and annual mean radiation data” have two possible meanings. We’re used to thinking of time correlation of spatial means. But it can equally mean spatial correlation of time means. Since they have cited a dataset of spatially distributed time mean temperatures, and used LISA to get the spatial correlations, it’s clear that they are using the second interpretation."

Nick was able to determine this from a read of the full paper, therefore, I requested confirmation and a copy of the full paper from the authors, received this morning. The authors confirm the paper shows a correlation between spatial UV-B and spatial mean annual temperature and that they did not test for temporal correlations. Thus, the abstract was incorrectly/misleadingly worded as finding

"UV-B surfaces were correlated with global mean temperature"

when it would have been more correct to state

"UV-B surfaces were correlated with spatial mean temperature"

as use of the term "global" to describe a spatial mean temperature is inappropriate.

Thus, based upon the now-clarified, albeit inappropriate, wording of the abstract, the claim of this post that UV-B has been demonstrated to be correlated to "global mean temperature" is withdrawn.

Nonetheless, there may or may not be a correlation between the two and it should be investigated for some of the following reasons:

1. Solar UV varies up to 100% over solar cycles

2. Solar UV greatly affects a) ozone production, which can also act as one of many solar amplification mechanismsb) temperatures of the stratosphere, mesosphere, and thermospherec) photosynthesis and other large effects on the biosphere as shown by this paper

3. UV is the most energetic portion of the solar spectrum, and penetrates the deepest into the ocean in comparison to the rest of the solar spectrum. Therefore, it has the greatest effect upon ocean heating compared to any other portion of the solar spectrum, and likely is more efficient in heating land as well.

4. For these reasons, and others, the various portions of the solar spectrum can have vastly differing effects on climate and change far more than the TSI. It is woefully inadequate to dismiss this by only incorporating the tiny 0.1% changes in TSI in climate models.